Interchangeable container with moveable side walls

ABSTRACT

The invention relates to a device for producing three-dimensional models.

CLAIM OF PRIORITY

This application is a national phase filing under 35 USC § 371 from PCTApplication serial number PCT/DE2014/000609 filed on Dec. 1, 2014, andclaims priority therefrom. This application further claims priority fromGerman Patent Application DE 10 2013 018 031.7 filed on Dec. 2, 2013.PCT Application Number PCT/DE2014/000609 and German Patent ApplicationNumber 10 2013 018 031.7 are each incorporated herein in theirentireties by reference.

DESCRIPTION

The invention relates to a device and its use in a method for producingthree-dimensional models.

A method for producing three-dimensional objects from computer data isdescribed in the European patent specification EP 0 431 924 B1. In thismethod, a particulate material is applied in a thin layer to a platform,and a binder material is selectively printed onto the particulatematerial, using a print head. The particle area onto which the binder isprinted sticks together and solidifies under the influence of the binderand, if necessary, an additional hardener. The platform is then loweredby a distance of one layer thickness into a build cylinder and providedwith a new layer of particulate material, which is also printed asdescribed above.

These steps are repeated until a certain, desired height of the objectis reached. A three-dimensional object is thereby produced from theprinted and solidified areas.

After it is completed, this object produced from solidified particulatematerial is embedded in loose particulate material and is subsequentlyremoved therefrom. This is done, for example, using an extractor. Thedesired objects remain afterward, from which powder deposits areremoved, e.g., by means of manual brushing.

Of all the layering techniques, 3D printing based on powdered materialsand the supply of liquid binder is the fastest method.

This method may be used to process different particulate materials,including natural biological raw materials, polymers, metals, ceramicsand sands (not an exhaustive list).

The machines used in methods of this type often contain a job box, whichcan be inserted into and removed from the 3D printing machine for thepurpose of increasing the machine runtimes. The job box may be removedfrom the machine for the purpose of freeing the components ofunsolidified material, i.e., to unpack them. Another job box may then beimmediately inserted into the machine, and printing may continue rightaway, avoiding unnecessary, unproductive machine down times. Job boxesof this type have a building platform to which the particulate materialis applied. This building platform is generally adjustable in height andis lowered during 3D printing until the printing process is completed.The desired layer thickness is adjusted by moving and positioning thebuilding platform.

The precise positioning of the building platform is extremely importantand crucial for the production of dimensionally accurate components. Notonly is the positioning of the building platform at the drive engagementpoint important, but a uniform positioning of all points of the buildingplatform also influences the construction accuracy. Possibledeformations of the building platform pose a problem to the precise andaccurate production of components.

A precise and even positioning, however, presents an enormous difficultyin large machines. The large dimensions result in high bending torques,which deform the building platform. If the building platform isreinforced accordingly, however, heavy weights, in turn, must bepositioned precisely. The various aspects of these problems reduce theachievable accuracy of the device or prevent an acceptable cost margin.

The forces and the resulting bending torques are caused by differentinfluences. First of all, the powder feedstock, which grows during thebuilding process, acts as an increasing planar load. Secondly, thegrowing feedstock presses against the walls of the build container.Reaction forces result here, which, in turn, act upon the buildingplatform. Forces are also produced by the seal, which seals the movingbuilding platform against the stationary side walls.

Approaches to the growing planar load are described in patentspecifications. For example, DE 10 2010 013 733 A1 discloses a device,in which the build container is designed as an immobile worktable. Thedevices for generating a new powder layer and for selectivesolidification are displaceable in the building direction of the device.The design of the building platform may be easily adapted to therigidity requirements. Because it is designed without walls, however,the device is limited in the range of materials that may be used.

The sealing forces may be influenced by structural measures. One optionis thus to use a build container which is equipped with a felt seal forthe purpose of reducing seal friction. Inflatable seals may also be usedto minimize the contact force.

The lateral rubbing action of the feedstock against the side walls is anunresolved problem in build containers or job boxes according to theprior art. According to the prior art, the effects of the forcesresulting therefrom are mitigated by structural measures. Buildcontainers are used whose driving points were selected for the purposeof minimizing deflection. In this case, planar loads may be taken intoaccount by the weight of the material and the friction effect, andlinear loads may be taken into account by the seal. Despite thisoptimization, more massive designs are created than would be necessaryto actually support the weight force.

An also structural measure for reducing the force effects is to shortenthe flux of force within the device. A passage through the buildcontainer wall is implemented, e.g., in DE 100 47 614 C2. This passageis sealed against through-flow of the particulate material by a belt ora flap. For heavy feedstocks, devices are provided with acorrespondingly large design. The approach using the flap is suitableonly for light-weight particulate material that applies very littlepressure to the wall.

When moving the building platform, in particular, a friction is producedlaterally, which results in stresses within the particulate applicationmaterial. Due to these stresses, movements may occur in the particulateapplication material, and the predetermined component points printed onthe basis of the CAD data may be displaced thereby. The spatial pointspresent in the component then ultimately deviate from the CAD data, andthe printed component no longer corresponds 1:1 to the data record. Theprinted component is thus inaccurate. This inaccuracy is based in largepart on the friction problem.

However, this problem has not been identified in the literature and inthe prior art as a problem and a cause of inaccurately producedcomponents. As a result, this problem has not been addressed to asatisfactory degree, nor are there any approaches thereto in theliterature and in the prior art.

The object of the invention is therefore to provide a device whichsolves the problems described above and, in particular, provides a jobbox, with the aid of which high-quality components may be produced witha high reproduction accuracy, and which makes available, in particularjob boxes having a reduced friction problem or an approach which avoidsor at least helps reduce the disadvantages of the prior art.

BRIEF DESCRIPTION OF THE INVENTION

The invention relates to a build container or job box, which makes itpossible to produce high-quality components and which has, inparticular, a reduced friction problem. This object is achieved by two,preferably three, advantageously four laterally situated, movable sidewalls, which are able to preferably move at the same speed as thebuilding platform in the job box according to the invention.

In another aspect, the invention relates to a 3D printing method, inwhich the build container (job box) according to the invention may beused.

DETAILED DESCRIPTION OF THE INVENTION

A number of terms in the invention are explained in greater detailbelow.

Within the meaning of the invention, “3D printing methods” relates toall methods known from the prior art which facilitate the constructionof components in three-dimensional molds and are compatible with thedescribed method components and devices. In particular, these arepowder-based methods, for example SLS (selective laser sintering).

Within the meaning of the invention, “selective binder application” or“selective binder system application” may take place after eachparticulate material application or irregularly, depending on therequirements of the molded body and for the purpose of optimizing theproduction of the molded body, i.e., non-linearly and not in parallelafter each particulate material application. “Selective binderapplication” or “selective binder system application” may thus be setindividually and during the course of producing the molded body.

“Molded body” or “component” within the meaning of the invention are allthree-dimensional objects that are produced with the aid of the methodaccording to the invention and/or the device according to the inventionand which have a nondeformability.

Any known 3D printing device that contains the necessary components maybe used as the “device” for carrying out the method according to theinvention. Common components include a coater, a build space, a meansfor moving the build space or other components, a dosing device and aheating means and other components which are known to those skilled inthe art and therefore do not need to be listed in greater detail here.

All materials known for powder-based 3D printing, in particular sands,ceramic powders, metal powders, plastics, wood particles, fibrousmaterials, celluloses and/or lactose powders, may be used as“particulate materials.” The particulate material is preferably a dry,free-flowing and a cohesive, firm powder.

“Build space” is the geometric place in which the particulate materialfeedstock grows during the build process by repeated coating withparticulate material. The build space is generally delimited by a base,the building platform, by walls and an open cover surface, the buildplane.

A “build container” or, in particular, a “job box” within the meaning ofthe invention implements a build space. As a result, it has a base,walls and an open access area, the build plane. The build containeralways includes parts which do not move relative to the frame of the 3Dprinting device. Removable build containers make it possible to operatethe machine more or less continuously. While the parts in a firstbuilding operation are being unpacked, new parts may be printed withinthe machine in a second build container.

The “printing and coater plane” is the abstraction of the location ofthe building process currently in progress. Since the dosing unit andthe coater are structurally moved in the device on a positioning unitwith shared components at nearly one height, the “printing and coaterplane” are viewed in this description as being situated at the upperedge of a newly applied layer.

The “building platform” moves relative to the printing and coater plane.This relative movement takes place during the building process ininterrupted movements in the layer thickness. It defines the layerthickness.

“Container wall” or “wall” or “side wall” designates a barrier to theparticulate material. The particulate material is unable to travel fromone side of the wall to the other. Walls within the meaning of theinvention may have a flexible or rigid design. The deflections for the“rigid” criterion are minor with respect to the workpiece tolerances ina given material system.

A “tribological pairing” within the meaning of the invention is amaterial contact whose coefficient of friction is significantly belowthat of two equal materials in contact or of the contact betweenparticulate material and a wall material.

A “seal” designates two structural elements which prevent a passage ofthe particulate material through contact points between walls movingrelative to each other or between walls and a building platform.

The invention, along with its preferred specific embodiments, isdescribed in greater detail below

The invention relates to a build container, in particular a job box, fora device for producing three-dimensional models by means of layering,which includes a build space on a building platform, which is adjustablein height within the build container and is preferably removabletherefrom, at least two side walls, which are designed in such a waythat during the displacement of the building platform, the kineticfriction between the constructed layers and the side walls is reduced oressentially avoided, the building platform and the at least two sidewalls being moved at the same speed.

In one aspect, the invention is the direct reduction of the forcesbetween the particulate material and the side wall in the buildcontainer. Different structural measures may be helpful for thispurpose. The avoidance of the relative movements also does not cause anyeffects of force in addition to gravity in the powder and may thus avoidundesirable settling of the powder cake.

As a result, it may be advantageously achieved that no or few forcesoccur which have a negative effect on the stability of the applied anddeposited layers, and the reproduction accuracy may thus be increased inthe printed components.

In one preferred specific embodiment of the invention, the buildcontainer is characterized in that 3 or 4 side walls are designed asdescribed above. The side walls of the build container are preferablymovable in the building direction. The movable side walls arefurthermore advantageously movable relative to two fixed side walls inthe build container.

The side walls are designed in such a way that they advantageously servethe purpose of the invention. The side walls are preferably designed tobe rigid with respect to the feedstock pressure. All reinforcements,cross-braces known to those skilled in the art may preferably be used.

In one preferred specific embodiment, the build container ischaracterized in that the side walls are not rigid with respect to thefeedstock pressure and are supported via additional side walls.Preferably at least one, preferably 2, 3 or 4, side wall(s) is/aredesigned to be flexible in one direction. It is furthermore preferredthat at least one, preferably 2, 3 or 4, side wall(s) is/are a segmentedand/or metallic wall and is/are designed to be flexible in onedirection.

In another preferred specific embodiment, the build container ischaracterized in that [sic; it] has a metal/plastic tribological pairingfor reducing the friction effect. The build container preferablyincludes at least one roller bearing for reducing the friction effect.The build container furthermore preferably includes a supported belt,which is flexible in all directions, as the side wall.

The build container may furthermore preferably include a belt made ofmultiple materials having an antifriction layer. A continuous belt ispreferably used as the side wall. This belt is particularly preferably afinite belt, and it is tensioned by means of springs or by the weightforce. The finite belt is preferably wound up in the upper area of thebuild container.

In other preferred specific embodiments, the invention relates, inparticular, to a device for producing a component (3D molded body),wherein (a) a particle layer is applied to a building platform (102) ina first step with the aid of a powder coater (101); (b) a binder (400)is selectively applied in a second step with the aid of a binder dosingdevice (100); (c) the applied layer or layers is/are subjected to a heattreatment in another step with the aid of a heat source (600); (d) thebuilding platform (102) is lowered by the thickness of one layer, or thepowder coater (101) and possibly additional device components is/areraised by the thickness of one layer; steps a) through d) are repeateduntil the component is built up.

According to the nature of particulate material (300), the resultingfeedstock constitutes a load for the build container and the buildingplatform. Characteristic pressure profiles (201), which are similar tohydrostatic pressures, occur on walls (200). Linear characteristics ofthe pressure over the build height do not occur in the static situation.However, if the powder is excited by mechanical vibrations, nearlyhydrostatic, i.e., linear, pressure characteristics occur.

The pressure loads on the container wall caused by the powder representforces normal to the wall. Once a movement perpendicular to thedirection of force occurs, reaction forces arise via the friction.

The flux of force usually closes over extensive parts of the device.FIG. 3 shows a sectional view of a possible device. The force arisesbetween container walls (200) and feedstock (300). Due to the feedstock,the force is conducted into container base (102). The course continuesthrough driving points (301), via coupling (302), to the Z-axis drive,which is usually designed as a lifting spindle (303). The latter isusually supported on the main frame of the device via a bearing (304).The flux of force closes over the build container retaining bolt, which,in turn, is mounted on the frame of the device, and via the buildcontainer wall.

Depending on the structural design, bendings and elongations whichinfluence the precision of the device occur due to the flux of force.According to the invention, the flux of force is not predominantlystructurally shortened, and the device does not have a load-optimizeddesign, but instead the effect of the force of the friction is minimizedduring relative movement.

The friction due to the direct contact between the wall and particulatematerial could be minimized by a coating. Abrasive particulatematerials, however, would quickly make this coating ineffective duringrelative movement. Even plastic powders have an abrasive effect.

A device which carries out the aforementioned steps for producing modelsinside a build container is one approach to avoiding relative movements.During the building process, the coating and printing unit (100, 101)travels out of the build container. The build container may then bereplaced in the upper end position. A device of this type has thedisadvantage that the coating unit (101) and dosing unit (100) partshave finite dimensions and cover not only the work area. This wouldunnecessarily enlarge the device. In addition, the acceleration ramps ofthe components must be taken into account, since their function iscarried out flawlessly only in the case of linear movement.

This technically unfavorable design may also be reduced, according tothe invention, to two walls positioned relative to the feedstock. FIG. 6shows an example of the build container design of a device of this type.

For this purpose, a U-shaped body is formed, which comprises two rigidwalls (400) and build platform (102). This body is moved between tworigid, frame-fixed walls (400), which are situated perpendicularly tothe walls of the U-shaped body. Seals (401), which prevent an outflow ofparticulate material, are mounted on the end faces of the body. In thisdevice, plane (701) of the new layers to be formed is always at theupper edge of the frame-fixed walls.

The coater and the dosing unit in this device may be moved through theresulting “shaft” and may be accelerated. The other function featuresare the same as those of a device having a conventional build container.

In this design, the forces on the moving walls do not result in anyfriction effect. The forces on the upright walls produce the samefrictional forces that also arise in a conventional design. In thearrangement of the overall structure according to the invention,however, the forces and the particularly harmful bending torques on thebuilding platform may be significantly reduced.

The limitations in the displacement area of the dosing unit and coaterare bothersome in a device of this type. To avoid this, the walls mustbe conceptually provided in the dosing and coater plane during thedownward movement of the building platform.

An effect of this type may be achieved during the first approach byusing a roller (700) having a flexible wall (402). The roller rollsalong the wall due to the movement of building platform (102).

A flexible wall (402) is deformed by the pressure of the feedstock. Toavoid jeopardizing the building process, the deformations must beminimized by structural measures. According to the invention, flexiblewall (402) is supported by a rigid wall (400). According to theinvention, the coefficient of friction between the contacting materialsmust be less than that between the rigid wall and the particulatematerial.

Typical material pairings according to the invention are metal/plasticcontacts or pairings as [sic; of] different metals. For example,flexible wall (402) made of metal may be designed as a thin sheet-metalband. Rigid wall (400) in this design is coated with plastic or brassstrips (900). The wall may also be designed as a plastic belt, which isrun off a metal surface.

The belt may preferably also be made of multiple materials. For example,a contact material to the particulate material may have a particularlyresistant design. The rigidity may be provided by a special strap. Anantifriction coating may be applied to the back.

Likewise, a flexible wall (402) may also slide on rollers (901).Powder-impermeable link chains are suitable for this purpose. Thefrictional forces may be further reduced with respect to tribologicalpairings. In terms of design, however, rollers of this type may besensible only when used in large devices.

The aforementioned device, having two walls which do not move relativeto the feedstock, may also be designed with four immobile walls. Adevice of this type would greatly reduce the frictional forces similarlyto the aforementioned device having 4 rigid, upright walls according tothe invention.

Other preferred aspects as well as an example of one preferred specificembodiment and advantages of the invention are discussed below.

Example of a preferred job box according to the invention

FIGS. 12 and 13 show a build container, which is particularlyadvantageous according to the invention.

The container is designed for a build volume of approximately 2,000liters. When using foundry molding materials, such as sand or chromeore, as the particulate materials, the feedstock weight may be up to4,500 kg. During the building process, 300 μm must be supplied with thebuilding platform as common layer thicknesses. The positioninguncertainty should be less than +/−30 μm for process-secureconstruction.

To reduce static deformations and minimize the effect of backlashes, thesequence of a layer application is as follows. The building platform isfirst lowered by an amount which is much greater than the targeted layerthickness, starting from the position of the last selectively solidifiedlayer. Only then is the building platform placed in the desiredposition. This position is one layer thickness lower that the last layeralready applied and solidified.

During the positioning, different components, such as the machine frameor the building platform, are deformed by the active forces. Thebuilding platform may then become stuck in the build container if it isnot sufficiently loaded by the powder feedstock, and the positioningmovement follows only after all backlashes have been resolved and thedeformation reaction forces of the components overcome the frictionalforces. This distance at least must be provided during lowering.

The building platform must then move upward into the predeterminedposition. The traveling distance here as well should at least pretensionthe device to the extent that stable conditions are achieved.

To safely account for this positioning uncertainty, the constantlygrowing weight force during the building process is less problematicthan the forces caused by feedstock friction. These forces not only growalong with the weight force, but they have an unpredictable nature, dueto the settling of the feedstock and the known stick-slip effect. Thepositioning uncertainty therefore increases markedly due to theseforces.

The device according to FIG. 12 has 2 fixed walls (400). These walls aremade of solid aluminum plates, which have recesses on the outer side forthe purpose of reducing the weight. The inner areas of the walls of thisbuild container have smooth, milled surfaces.

Building platform (102) has a greatly ribbed design, due to the heavyweight forces. The building platform typically has a rectangular shapedefining long sides (1212) and short sides (1210) of the buildcontainer. The drive engagement takes place on the short sides in eachcase. The long sides are equipped with a seal. The seal has a two-partdesign. To set an even contact pressure and thus to form a secure seal,there is a spring element and a seal, which is able to slide smoothlyalong the walls of the build container. The spring element is a cord,which has a rectangular cross section and is made of silicone foam. Theseal is a felt cord having a rectangular cross section.

In its lower end position, the building platform is in the buildcontainer. This ensures that the build container is able to be removedfrom the machine when the drive engagements are released.

The short sides are fixedly connected to flexible container wall (402).

In this build container, flexible wall (402) is made of an aluminum linkchain (1202). The latter comprises plates which are 20 mm wide and whichare interconnected by rubber strips.

The short side wall has a rigid wall (400) on the inside. The latter isdesigned as a welded frame made of rectangular tube profiles. Theseprofiles support plastic rails (900) on the inside of the buildcontainer. These rails minimize friction.

This wall supports a return roller (700) on its upper end. Aluminum linkchain (1202) is guided over this roller. Weights (1300) are mounted onaluminum link chain (1202) on the side of the wall facing away from thecontainer interior. These weights ensure a taught chain during theupward travel.

The drive engagements are guided around this external link chain. As aresult, they are easy to contact by the 3D printing device.

The sealing action between the aluminum link chain and rigid wall (400)on the long side of the build container is once again achieved by a feltcord. A recess, which guides the sealing cord, is present on the plateof the long side.

The upper edge of the build container is equipped with profiles in thearea of the return roller, which rectangularly form the containerinterior. The friction which occurs here may be disregarded, since thefeedstock pressure is still very low in this position.

The long and short walls form a frame, which, together with the buildingplatform, represents a container. The latter is reinforced by a floorstructure (1201). Skids are additionally mounted on the undersidethereof to enable the container to move with the aid of a rollertransport system.

Devices for connecting the container and the 3D device are present onthe short walls. These devices may be locked after the container isinserted. The container is thus positioned and locked in place.

The build container is lined with additional metal sheets (1200) for thepurpose of sealing against external contamination.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: shows a schematic representation of the components of apowder-based 3D printer in a sectional isometric view;

FIG. 2: shows a schematic representation of the effect of the force ofthe powder feedstock;

FIG. 3: shows a diagram of the flux of force in a device according tothe prior art;

FIG. 4: shows a representation of a rigid and a flexible container wall;

FIG. 5: shows a device, including a build container which has four rigidwalls which are not moved relative to the feedstock;

FIG. 6: shows a design of a build container having two rigid walls whichare not moved relative to the feedstock and two rigid walls which aremoved relative to the feedstock;

FIG. 7: shows a diagram of the avoidance of walls in the displacementarea of the dosing unit and coater due to flexible walls;

FIG. 8: shows a diagram of the discharge of compressive forces viaconsecutively connected walls.

FIG. 9: shows the minimizing of the forces through the use of atribological pairing; minimizing of the forces through the use ofrollers;

FIG. 10: shows a build container having two flexible walls which are notmoved relative to the feedstock;

FIG. 11: shows a build container having four flexible walls which arenot moved relative to the feedstock;

FIG. 12: shows a sectional representation of a build container havingflexible walls which are not moved relative to the feedstock;

FIG. 13: shows design details of a build container having flexible wallswhich are not moved relative to the feedstock.

LIST OF REFERENCE NUMERALS

-   -   100 Binder dosing device    -   101 Powder coater    -   102 Building platform    -   103 Component (3D molded part)    -   104 Build space boundary    -   107 Powder layers    -   200 Wall    -   201 Force profile    -   300 Particulate material    -   301 Driving point    -   302 Coupling    -   303 Lifting spindle    -   304 Bearing    -   400 Rigid wall    -   401 (Felt) seal    -   402 Flexible wall    -   500 Positioning unit    -   501 Guides    -   700 Return roller    -   701 Printing and coater plane    -   800 Free deflection    -   900 Sliding surface    -   901 Rollers    -   1200 Housing    -   1201 Base    -   1202 Aluminum link chain    -   1210 Short side    -   1212 Long side    -   1300 Counter-weight

What is claimed is:
 1. A build container for a device for producingthree-dimensional objects by layering, comprising: a build space on abuilding platform having a rectangular shape defining short sides andlong sides of the build container, wherein the build space is adjustablein a height and is within the build container; wherein during adisplacement of the building platform to adjust the height of the buildspace, a kinetic friction between constructed layers and at least twoside walls is reduced or essentially avoided, the building platform andthe at least two side walls being moved at the same speed, wherein thebuild container includes a drive engagement on each of the short sidesfor attaching to a Z-axis drive unit, and wherein the only movement ofthe build platform during building of the three-dimensional objects is avertical movement.
 2. The build container of claim 1, wherein the atleast two side walls includes 3 or 4 side walls.
 3. The build containerof claim 1, wherein the at least two side walls of a build container aremovable in the build direction.
 4. The build container of claim 1,wherein the at least two side walls are not rigid with respect to aparticulate feedstock pressure and are supported via additional sidewalls.
 5. The build container of claim 1, wherein at least one of the atleast two side walls is designed to be flexible in one direction.
 6. Thebuild container of claim 1, wherein the at least two side walls are asegmented wall and/or a metallic wall and are designed to be flexible inone direction.
 7. The build container of claim 1, wherein ametal/plastic tribological pairing is used to reduce the frictioneffect.
 8. The build container of claim 1, wherein a supported belt,which is flexible in all directions, is used as at least one of the atleast two of the side walls.
 9. The build container of claim 1, whereina continuous belt is used as at least one of the at least two sidewalls.
 10. The build container of claim 1, wherein a finite belt is usedas at least one of the at least two side walls and is tensioned by oneor more springs or a weight force.
 11. The build container of claim 1,wherein the build container is capable of attaching to and then removingfrom a 3D printing device by engaging and disengaging the 3D printingdevice with the drive engagement, wherein the 3D printing deviceincluding a coater unit and a print head for constructing layers ofparticulate material and selectively printing a binder.
 12. The buildcontainer of claim 3, wherein the at least two side walls of the buildcontainer are displaceable relative to two fixed side walls.
 13. Thebuild container of claim 12, wherein the at least two side walls of thebuild container are rigid with respect to a particulate feedstockpressure.
 14. The build container of claim 5, wherein the at least twoside walls include four side walls that are designed to be flexible inone direction.
 15. The build container of claim 6, wherein the at leasttwo side walls include three or four side walls.
 16. The build containerof claim 1, wherein the build container includes an additional driveengagement positioned for attaching to an additional Z-axis drive uniton a different side of the build container.
 17. A device forconstructing three-dimensional objects comprising the build container ofclaim 1, a coating device for applying a particulate feedstock materialin layers over the build platform, and the Z axis drive unit on a sideof the build container and attached to the build container by the driveengagement.
 18. The device of claim 17, wherein at least one rollerbearing is used to reduce the kinetic friction.
 19. The device of claim17, wherein the device includes a belt made of multiple materials andincludes an antifriction layer.
 20. The device of claim 17, wherein afinite belt is wound up in an upper area of the build container.
 21. Thedevice of claim 17, wherein the Z-axis drive unit is a lifting spindle.22. A method for producing three-dimensional objects by layeringcomprising the steps of: constructing layers of a three-dimensionalobject with a coater for applying particulate material; wherein betweena process of constructing two layers, a build platform is displaced toadjust a height of a build space within a build container, the buildcontainer is adjustable in height and have a plurality of side walls;wherein during a step of displacing the building platform, kineticfriction between the constructed layers and at least two side walls ofthe plurality of side walls is reduced or essentially avoided, whereinthe building platform and the at least two side walls are moved at thesame speed; wherein a Z-axis drive unit positioned on a side of thebuild container drives the build container in a vertical direction,wherein the Z-axis drive unit is attached to a drive engagement of thebuild container, and wherein the only movement of the build platformduring building of the three-dimensional objects is the verticalmovement.
 23. The device of claim 22, wherein the Z-axis drive unit is alifting spindle.
 24. The method of claim 22, wherein the methodcomprises a step of selectively applying a binder material over a layerof particulate material.